In electrostatographic reproduction apparatus, such as electrophotographic copier/duplicators, printers, or the like, a light image of an original document to be printed or copied is typically recorded by either digital or analog devices as an electrostatic latent image upon a photosensitive member. Subsequently, the latent image is rendered visible (i.e., developed) by application of electrostatically charged marking particles, commonly referred to as toner. The developed toner image can be either fixed directly upon the photosensitive member, or transferred from the photosensitive member to another support substrate, or receiver member, such as a sheet of plain paper, with subsequent affixing of the toner image thereto.
In order to fix or otherwise fuse the toner material onto a receiver member permanently, it is generally necessary to apply heat so as to elevate the toner material to a temperature at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent into the fibers or pores of the receiver member or to otherwise adhere to the surface thereof. Thereafter, as the toner material cools, solidification occurs causing the toner material to be bound firmly to the receiver member.
One method for thermal fusing of toner images onto a receiver member has been to pass the receiver member with an unfused toner image thereon between a nip formed by a pair of opposed roller members that are in contact with each other, wherein at least one of the roller members is heated. During operation of a fusing system of this type, the receiver member to which the toner image is electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roller thereby to affect heating of the toner image within the nip. Typical of such fusing devices are two roller systems wherein a fuser roller is coated with an adhesive material, such as a silicone rubber; other low surface energy elastomers, such as a Viton® fluoroelastomers available from E.I. DuPont De Nemours of Wilmington, Del.; or other low surface energy material, such as tetrafluoroethylene polymer resins like, for example, Teflon® resins also sold by DuPont.
In the foregoing fusing systems, however, since the toner image is tackified by heat, it frequently happens that a part of the image carried on the receiver member will be retained by the heated fuser roller and not penetrate into the receiver member surface. This tackified material can stick to the surface of the fusing roller and come in contact with a subsequent receiver member bearing another toner image to be fused. Thus, a tackified image, which has been partially removed from a first receiver member, may thereafter transfer to a subsequent second receiver member in non-image portions of the second receiver member. In addition, a portion of the tackified image of the second receiver member may also adhere to the heated fuser roller. In this way and with the fusing of subsequent sheets bearing toner images, the fuser roller can eventually become thoroughly contaminated and unusable, thereby requiring replacement of the fuser roller itself. In addition, since the fuser roller continues to rotate when there is no substrate bearing a toner image to be fused, toner that may be adhered to the fuser roller can be transferred from the fuser roller to the pressure roller, and also to other rollers and components associated with the fuser system, thereby contaminating the overall fuser system. The foregoing conditions are referred to generally in the printing/copying art as “offset”. Attempts have been made to control heat transfer to the toner and thereby control offset. However, even with adhesive surfaces provided by the silicone elastomers and the other materials mentioned hereinabove, this has not been entirely successful.
It has also been proposed to provide toner release agents such as silicone oil, and in particular poly(organosiloxane) oils like poly(dimethylsiloxane), that are applied to the surface of the fuser roller to act as a polymeric release agent and thereby reduce offset. The use of such release agents is reported, for example, in U.S. Pat. Nos. 3,964,431 and 4,056,706, the teachings of which are incorporated herein by reference. These release agents possess a relatively low surface energy and have been found generally suitable for use in a heated fuser roller environment. In practice, a thin layer of poly(organosiloxane) oil (also referenced as silicone oil hereinafter) release agent is applied to the surface of the heated fuser roller to form an interface between the fuser roller surface and the toner image carried on the support material. Thus, a low surface energy, easily parted layer is presented to the toners that pass through the fuser toning nip and thereby reduces the amount of toner which offsets to the fuser roller surface.
Various methods are known for applying release agent materials to a fuser member such as a heated fuser roll. One such system comprises a Release Agent Management (RAM) system including a donor roll that contacts the fuser member to which the oil or release agent material is applied. The donor roll also contacts a metering roll, which conveys the oil from a supply of oil to the donor roll. With such a system, it is customary to use a metering blade to meter the silicone oil or other suitable release agent material to a desired thickness onto a metering roll. In the fusing of monochrome (i.e. black on a conventional imaging substrate) the uniformity of the oil layer on the metering roll is not so critical compared to that required for color toner images, particularly, those associated with transparency substrate materials used for optically projecting the color images.